1. Field of the Invention
The present invention relates to a process for producing an electrolytic capacitor. More particularly, the present invention relates to a process for producing an electrolytic capacitor by utilizing a photosensitive polymer resin to provide very thin spacer layers interposed between an anode metal foil and a cathode metal foil. The process of the present invention is useful to provide a small size, high efficiency electrolytic capacitor without using a paper spacer.
2. Description of the Related Art
It is known to produce a conventional electrolytic capacitor by connecting a pair of electrode tabs consisting of, for example, aluminum, to a pair of anode and cathode metal foils consisting of, for example, aluminum, superimposing alternately two spacers and the anode and cathode metal foils, in the order of, for example, the anode foil, a spacer, the cathode foil, and a spacer, by winding the resultant laminate to provide a capacitor element, and by impregnating the capacitor element with an electrolyte.
The electrolyte-impregnated capacitor element is placed in a case and an opening of the case is hermetically sealed.
The purpose of interposing the spacers between the anode and cathode metal foils is to space and insulate the anode and cathode from each other and to hold the electrolyte. That is, spacers are important elements for the electrolytic capacitor.
In conventional electrolytic capacitors, the spacers are usually made from kraft paper.
Conventional spacers consisting of kraft paper make the production of a small size capacitor difficult due to the following features of the kraft paper:
(1) The kraft paper has a relatively large density of from 0.3 to 0.8 g/cm.sup.3. PA1 (2) In the kraft paper, pulp fibers are in the depressed flat form. Therefore, the kraft paper exhibits a relatively high apparent specific resistance and an unsatisfactory tan .delta. (tangent of loss angle) property. PA1 (3) It is difficult to make the thickness of the kraft paper less than 30 .mu.m due to restrictions in papermaking technology.
In order to eliminate the disadvantages of the kraft paper spacer, it has been attempted to replace the kraft paper with a low density manila paper. Capacitors containing manila paper spacers exhibit an improved tan .delta. property and are produced and used in a limited field.
However, manila paper is very expensive, being priced several times more than kraft paper. Also, in order to make the mechanical strength of manila paper high enough to resist the capacitor-producing process, especially the winding procedure, the manila paper must have a relatively large thickness of 40 .mu.m or more. This requirement causes the resultant capacitor to be of a relatively large size.
Additionally, the use of paper spacers, whether of kraft paper or of manila paper, complicates and reduces the efficiency of the process and apparatus for arranging the anode and cathode metal foils and the spacers to provide a laminate and for winding the laminate.